A 29-year-old male, otherwise healthy with no past medical history, presented to the hospital after a twoday history of pleuritic chest pain with a fever. He had received his first dose of the mRNA-1273 coronavirus disease (COVID-19) vaccine (Moderna) two months prior without any adverse reactions. He received his second dose approximately 24 hours before symptom onset and hospital presentation. Work-up was unremarkable for respiratory, autoimmune, and rheumatological etiologies. The patient was found to have electrocardiogram features and symptoms in keeping with pericarditis, C-reactive protein elevation, and a peak high-sensitivity troponin level of 9,992 ng/L suggestive of a component of myocarditis. A dilemma arose regarding whether this patient should be diagnosed with perimyocarditis or myopericarditis, terms often used interchangeably without proper reference to the primary pathology, which can ultimately affect management. A subsequent echocardiogram was unremarkable, with a normal left ventricular systolic function, but cardiac resonance imaging revealed myocardial edema suggestive of myocarditis. Without convincing evidence for an alternative explanation after an extensive work-up of ischemic, autoimmune, rheumatological, and infectious etiologies, this patient was diagnosed with COVID-19 mRNA vaccineinduced myopericarditis. The patient fully recovered after receiving a treatment course of ibuprofen and colchicine. This case explores how the diagnosis of COVID-19 vaccine-induced myopericarditis was made and treated using an evidence-based approach, highlighting its differentiation from perimyocarditis.
